This invention pertains to porous metal oxide supported carbon-coated catalysts which have improved porosity, surface area, and particle strength. It also pertains to methods for producing such supported carbon-coated catalysts and their use in catalytic reaction processes principally in ebullated bed reactors.
Carbon based catalysts are generally known, for example, U.S. Pat. No. 3,793,224 to Cooper, U.S. Pat. No. 3,859,421 to Hucke and U.S. Pat. No. 3,978,000 to Schmidt, et al disclose methods for producing carbon based catalysts in which the support material used is primarily carbon. Activated carbon-substrate catalysts are known to have high activity and high surface area, but also have low density, low strength, and high attrition of the catalyst particles. One of the major difficulties in the use of such carbon-based catalysts in reactors containing fluidized and ebullated type catalyst beds is the relatively low density and low cohesiveness of such catalysts. This makes it difficult to retain the catalyst particles in a fluidized or ebullated bed in a reactor, and to prevent undesired catalyst attrition and carryover from the reactor to downstream process equipment. Also, the particle strength and attrition resistance of such carbon based catalysts is undesirably low, leading to costly high losses of catalyst due to attrition of the particles during such catalytic processing operations on hydrocarbon feedstocks.
It is known that activity of gamma-alumina substrate catalyst increases with increase in its pore volume and surface area. However, due to the low particle strength and low attrition resistance of such high pore volume catalysts, there is a practical limitation on maximum pore volume and surface area attainable for such catalysts. In our development work with catalyst leading to the present invention, it was noticed that carbon coatings on various catalysts results in a significant increase in catalyst strength and attrition resistance characteristics. Also, initial carbon coating tends to inhibit additional deposition of carbon on the catalyst, and consequently results in less deactivation of the catalyst during hydrocarbon processing operations. Thus, the catalyst maximum pore size for supported carbon-coated catalysts can be larger and the catalyst more effective in hydroconverting macromolecules having more than two rings.
It was found in our studies of spent catalyst regeneration, that spent catalyst having 10-20 W % carbon laydown and metals deposits can be treated with dilute acid solutions to substantially remove the metal deposits, after which the treated used catalyst will then perform generally about as well as a fresh catalyst at similar operating conditions, as was disclosed in U.S. Pat. Nos. 4,454,240 and 4,595,666 to Ganguli. It appears that the acid treatment removes the metallic constituents which are deposited on the catalyst along with the carbon, and thereby opens the pores located within the carbon and substrate matrix. Thus, the used catalyst treated to remove metal deposits has performance which is substantially equal to that of fresh catalyst. Although U.S. Pat. No. 3,446,865 to Roth et al has disclosed a supported carbon-coated catalyst, it does not provide adequate pore volume and surface area characteristics needed for many operations, such as catalytic hydrogenation of heavy hydrocarbon feedstocks.
It has now been unexpectedly found that by using separate controlled catalyst treatment procedures, improved fresh composite metal oxide supported carbon-coated catalysts can be produced having improved porosity, particle strength and catalytic activity. This supported carbon-coated catalyst structure permits successful use of such improved carbon-coated catalysts in fluidized and ebullated bed process applications with minimal attrition of the catalyst particles. Also, catalysts which are intended for use in process applications in which carbon laydown on the catalyst is not a normal process occurrence, such as in liquid phase methanation and other Fischer-Tropsch reactions and in the oxidation of organic vapors, can be advantageously strengthened and improved in catalytic activity and useful life using this carbon-coating catalyst production method.